I think if u look closely at all the goals he scored, majority of those came from disputed decisions such as offsides and fouls.
I dare to say that he cant dribble at all. The only goal i remembered him scoring via dribbling was against Fulham and their goalie at that time was Van der Sar! How ironic!

I think he can be replaced easily.
Jus ask the strikers to lurk in offside position, when the ball is about to pass to him, stay in line with the defenders and u can score many goals.
I don't even remember seeing him scoring a header before.
All of his goals seems to be super tyco or no one marking him.
Sorry to be critical here but i don't like his playing style since the very first season he joined. He disrupted United fast pace attacking strategy because he's too slow and always like to hog onto the ball.
Seriously, United's attacks will be much efficient if Saha can improve on his passing cos to me, Saha is a much better striker in terms of his pace and strength.
But Ruud will always be a United legend.

Cheers.
C.K